What means let y = &5; ??

Hey, I'm new in the forum and in the language.

Last week I started to read the Rust book, and in page 159 I have this:

let y = &5;

//This is the same as `let _y = 5; let y = &_y`

I understand the concept of reference, but I don't get it the &5.
In the second example we have an inmutable \_y with a 5, and a y with a reference of \_y (so y it's 5)

I can't see the same in the first example.

Greeting for Argentina